(a) Field of the Invention:
The present invention relates to a binary-coding apparatus and method for video signals which are used in an optical character reader facsimile, etc., and more particularly to a video signal binary-coding circuit optimally and effectively usable in producing binary-coded white and black-level signals from video signals derived from hand-written or printed dark characters and the like to prevent the images of such characters from being smudged dark when being reproduced as a result of the binary-coded black-level signal abnormally increasing.
(b) Related Art Statement:
In the prior-art video signal binary-coding circuit, a video signal is sliced at three different levels. A video signal at a level higher than the upper and middle slice levels is converted into the black level, a video signal at a level lower than the lower slice level is converted into the white level, and a video signal at an intermediate level, between the middle and lower slice levels, is converted into the white or black level depending on the surrounding condition. A video signal at an intermediate level between the above-mentioned middle and lower slice levels is binary-coded taking into account the surrounding condition, using a mask of 3 bits by 3 scans, and is converted into the white level if in the surrounding condition a video signal at a level higher than the upper slice level is found, or into the black level if no such video signal exists. The reason why the video signal at the intermediate level between the middle and lower slice levels is binary-coded in accordance with the surrounding condition, namely, in determining the existence of the black or white level is that the black and white levels are balanced with each other to optimize the binary-coded signal. The inventions related with the above-mentioned prior-art video signal binary-coding technique are disclosed, for example, in the Unexamined Patent Publications (Kokai) Nos. 57-27376, 57-81687 and 58-109979.
However, when the above mentioned prior-art video-signal binary-coding circuit is used to binary-code video signals derived from dark characters written by hand or printed by a laser beam printer (LBP), the image reproduced using the binary-coded signals will be smudged dark. Namely, the conventional techniques of video signal binary-coding are disadvantageous in that any hand-written or printed dark characters are binary-coded as inclined to the black level because the balance between the black and white levels is lost.